Corrosion inhibitor for methoxypropanol

ABSTRACT

THE CORROSIVE EFFECT OF METHOXYPROPANOL IS INHIBITED BY A THREE COMPONENT MIXTURE OF (1) AN ALKALI METAL NITRITE, (2) A PIPERAZINE, AND (3) BENZOTRIAZOLE.

United States Patent O 3,553,137 CORROSION INHIBITORS FOR METHOXYPROPANOL Conrad D. Woods, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Sept. 29, 1967, Ser. No. 671,588 Int. Cl. C09k 3/02; C2315 11/14, 11/18 US. Cl. 252-75 10 Claims ABSTRACT OF THE DISCLOSURE The corrosive effect of methoxypropanol is inhibited by a three component mixture of (1) an alkali metal nitrite, (2) a piperazine, and (3) benzotriazole.

BACKGROUND OF THE INVENTION Antifreeze fluid is usually essentially ethylene glycol, though lower alkanols are used to some extent. A combination of several corrosion inhibitors is added because a typical engine contains a variety of metals in contact with the fluid and no one inhibitor will protect all these metals. A great variety of inhibitors has been suggested in the art; these include the metal borates, phosphates, arsenates, arsenites, molybdates, chromates, nitrates, nitrites, amines, piperazines, benzothiazole, and benzotriazole, and some of their combinations. Methoxypropanol has also proven to be suitable as a heat transfer agent but, in itself, it is corrosive to the commonly used cooling system metals.

SUMMARY OF THE INVENTION It has now been discovered that a three component system comprising an alkali metal nitrite, a piperazine and benzotriazole is a very effective corrosion inhibitor for methoxypropanol. By the latter term I means to include both Z-methoxy-l-propanol and 1-methoxy-2-propanol. The commercially available material is predominantly the latter but contains a small proportion of the former.

According to this invention, the corrosiveness of methoxypropanol on the common metals of construction, particularly those used in heat-exchangers, is inhibited by dissolving in the methoxypropanol a small but effective amount of a corrosion-inhibiting composition comprising an alkali metal nitrite, a piperazine, and benzotriazole.

The alkali metal nitrite can be sodium nitrite, potassium nitrite, or the other alkali metal nitrites.

The piperazine compound can be piperazine itself, an alkylpiperazine wherein the alkyl group contains up to eight carbon atoms, or an amino-alkylpiperazine wherein the alkyl group contains up to eight carbon atoms. Examples of alkyl or amino-alkylpiperazines which are useful are Z-methylpiperazine, N-butylpiperazine, N-(2- aminoethyl)piperazine, and N-(3-aminopropyl)piperazine.

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TABLE I.-CORROSION INHIBITOR COM- POSITION Percent by weight Useful Preferred Components Plperazine compound Benzotriazole Alkali metal nitrite In formulating an inhibited composition, such as one suitable for use as a heat-transfer medium, the above inhibitor system is dissolved in the methoxypropanol in an effective concentration, suitably about 0.5 to 3.0% by weight. This is an especially small weight percent of inhibitor and thus presents an economical concentrate. As optional additives there may also be included dyes, acidbase indicators, water-pump lubricants, antifoam agents, or other conventional inhibitors or additives but this invention does not concern them. The above composition may be diluted with water, suitably to a concentration of from 30 to by volume, for use as an automotive antifreeze. The undiluted material is also useful as a heattransfer medium.

DESCRIPTION OF PREFERRED EMBODIMENTS The practice of our invention is illustrated by the following example.

An inhibited methoxypropanol composition was prepared by blending the following ingredients. The concentration is given in weight percent based on the total mixture.

Component: Weight percent Methoxypropanol 98.3 Piperazine 1.0 Benzotriazole 0.1 Sodium nitrite 0.1 Water 1 0.5

Water was added so as to facilitate the solubility of the nitrite; its presence is not necessary in the antifreeze concentrate. I

The above composition was tested for corrosiveness according to the standard glassware test procedures for automotive antifreezes described in the following methods: ASTM D1384, General Motors Corp. GM 1899M, and Ford Motor Co. BLl-l, each sample being diluted to 33 /3 by volume, as specified in the methods.

Also, the composition was tested according to the General Motors Corp. simulated service test (G.M. 1899M) procedure. The corrosion loss in mg./ sq. in. is reported 'below in Table II.

TABLE II.CORROSION TESTS Corrosion loss mgs./sq. in.

Observed G.M. simulated G.M. glassware service Allowable Observed Ford glassware Allowable ASTM

Observed Observed Coppen S d A1uminum-- 3 I clairn.: v. 1. A corrosion inhibitor comprising:

Component: Percentage by weight (a) Benzotriazole 1-20 (b) Alkali metal nitrite 1-20 (c) Piperazine, alklypiperazine or aminoalkylpiperazine wherein the alkyl or aminoalkyl moiety contains 1-8 carbon atoms Balance all percentages being based upon the total weight of (a), (b) and (c).

2. A corrosion inhibitor as defined in claim 1 comprising:

Component: Percent by weight (a) 8-12 (b) 8-12 Balance 3. A corrosion inhibitor as defined in claim 1 wherein the piperazine compound is an alkylpiperazine having up to eight carbon atoms in the alkyl group.

4. A corrosion inhibitor as defined in claim 1 wherein the piperazine compound is an amino-alkylpiperazine compound having up to eight carbon atoms in the alkyl group.

5. A corrosion inhibitor as defined in claim 1 wherein the piperazine compound is piperazine.

6. A corrosion inhibitor as defined in claim 1 wherein the alkali metal nitrite is sodium nitrite.

7. An anticorros-ive composition consisting essentially of methoxypropanol containing a small but effective proportion of a corrosion inhibitor as defined in claim 1.

8. A composition as defined in claim 7 wherein the corrosion inhibitor comprises from 0.5 to 3.0% by weight of the composition, based on the methoxypropanol. I

9. A composition as defined in claim 8 wherein the corrosion inhibitor comprises:

Component: Percent by weight (a) 8-12 (b) 8-12 (c) Balance 10. An antifreeze composition consisting essentially of the composition as defined in claim 2 and water wherein the water comprises from 30 to by volume of the fluid.

References Cited UNITED STATES PATENTS 1,780,927 11/1930 Jordan 25273 2,164,564- 7/1939 Britton, et a1. 25277 3,291,741 12/1966 Monroe, et a1. 252-76 3,414,519 12/1968 Beynon 252-75 US. Cl. X.R. 

